Electrostatic surface cleaning

ABSTRACT

Embodiments of the present invention generally provide apparatus and methods for cleaning a substrate, such as a mask. One embodiment of the present invention provides an apparatus for cleaning a substrate comprising a substrate support configured to receive and support the substrate, a collecting tip connected with an electrostatic power source, wherein the collecting tip is configured to pickup particles on a surface of the substrate using electrostatic force, and an indexing mechanism configured to provide relative movement between the collecting tip and the substrate support.

BACKGROUND

1. Field

Embodiments of the present invention generally relate to methods and apparatus for cleaning a surface. Particularly, embodiments of the present invention provide methods and apparatus for removing particles from a surface of a substrate or a mask during semiconductor processing.

2. Description of the Related Art

As the trend continues to reduce the size of semiconductor devices, the minimum particle size to be removed from substrates and masks also decreases. For example, in extreme ultraviolet lithography (EUVL), feature sizes can be 65 nm, 45 nm, 32 nm, or 22 nm, and the particles size limits are usually as small as 0.8 times the feature sizes.

Various methods may be used to remove particles from substrates or masks. For example, in one method, a substrate or mask is irradiated by a laser with sufficient energy to release the particles, while an inert gas flows across the wafer surface to carry away the released particles. In another method an energy transfer medium, typically a fluid, is interposed between each particle to be removed and the surface. The medium is irradiated with laser energy and absorbs sufficient energy to cause explosive evaporation, thereby dislodging the particles.

However, the current methods are either limited in applications or complicated to apply.

Therefore, there is a need for methods and apparatus to cleaning particles of small sizes from a surface of a substrate or a mask.

SUMMARY

Embodiments of the present invention generally provide apparatus and methods for cleaning a substrate or a mask. Particularly, the embodiments of the present invention provide apparatus and methods for removing particles from a substrate or a mask using electrostatic force.

One embodiment of the present invention provides an apparatus for cleaning a substrate or a mask comprising a substrate support configured to receive and support the substrate or the mask, a collecting tip connected with an electrostatic power source, wherein the collecting tip is configured to pick up particles on a surface of the substrate or the mask using electrostatic force, and an indexing mechanism configured to provide relative movement between the collecting tip and the substrate support.

Another embodiment of the present invention provides an apparatus for removing particles from a substrate comprising a substrate support configured to receive and support the substrate, a probe assembly configured to remove particles from the substrate, wherein the probe assembly comprises an arm having a free end and a fixed end, wherein the free end is movably disposed above the substrate support, a collecting tip mounted near the free end of the arm, and an electrostatic power source coupled to the collecting tip, wherein the electrostatic power source is configured to provide an electrostatic force to the collecting tip so that the collecting tip can remove particles from the substrate.

Yet another embodiment of the present invention provides a method configured for cleaning a mask or a substrate comprising providing a collecting tip configured to pick up particles from the mask or the substrate, applying an electrostatic force to the collecting tip, and moving the collecting tip towards the particles on the mask or the substrate to pick up the particles.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of embodiments of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 schematically illustrates a side view of a cleaning station in accordance with one embodiment of the present invention.

FIGS. 2A-2B schematically illustrate enlarged views of a collecting tip during a cleaning process in accordance with one embodiment of the present invention.

FIG. 3 schematically illustrates a perspective view of a cleaning station in accordance with one embodiment of the present invention.

FIG. 4 schematically illustrates a perspective view of a cleaning station in accordance with another embodiment of the present invention.

FIG. 5 is a flow chart showing a cleaning process in accordance with one embodiment of the present invention.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DETAILED DESCRIPTION

Embodiments of the present invention provide apparatus and methods for removing particles from a substrate or a mask using electrostatic force. In one embodiment, a collecting tip is coupled to an electrostatic power source and is configured to pick up particles from a substrate or a mask using electrostatic force when approaching the particles. In one embodiment, the collecting tip has a tapered end which has a diameter similar to size of the target particles. In one embodiment, the tapered end is slightly larger than the particles. In one embodiment, the target particles are those larger than 80 percent of critical size of the features on the substrate or mask being cleaned. Embodiments of the present invention further provide an indexing mechanism configured to generate relative movement between the collecting tip and the substrate or mask so that the entire surface of the substrate or mask may be cleaned.

FIG. 1 schematically illustrates a side view of a cleaning station 100 in accordance with one embodiment of the present invention. The cleaning station 100 may be configured to clean a substrate or a mask alone or combined with other cleaning processes. For example, the cleaning station 100 may be used to clean masks or substrates after wet cleaning during pattern generation.

The cleaning station 100 generally comprises a collecting assembly 103 disposed above a substrate support 101 configured to support a substrate/mask 102 thereon. In one embodiment, the collecting assembly 103 comprises a collecting tip 104 mounted on a mounting arm 109. The collecting tip 104 has a tapered end 105 free from the mounting arm 109 and facing the substrate/mask 102. The collecting tip 104 is electrically conductive and is coupled to an electrostatic source 107.

The electrostatic source 107 generally comprises an electrostatic generator configured to generate high voltages using either friction or electrostatic induction to accumulate electric charges. During cleaning, the collecting tip 104 is charged with electrostatic charges which generate electrostatic force to attract loose particles.

FIGS. 2A-2B schematically illustrate enlarged views of the collecting tip 104 during a cleaning process in accordance with one embodiment of the present invention. As shown in FIG. 2A, an electrostatic field 110 is generated around the tapered end 105 of the collecting tip 104 when the electrostatic source 107 provides electrostatic charges to the collecting tip 104. As shown in FIG. 2A, particles 106 under the influence of the electrostatic field 110 may be picked up by the collecting tip 104, thus clearing up from the surface of the substrate/mask 102. During the cleaning process, it is not necessary for the collecting tip 104 to contact the substrate/mask 102, thus preventing further contamination.

The collecting tip 104 may be charged positively or negatively. In one embodiment, the electrostatic charge applied to the collecting tip 104 may be in a range between about 50 volts to about 250 volts. In another embodiment, the electrostatic charge applied to the collecting tip 104 may be between about 50 volts to about 100 volts.

In semiconductor manufacturing, the size of the particles to be removed is generally determined by the critical dimension of the features. For example, for a mask to be used in photolithography, particles smaller than 0.8 times of technology node may be tolerable. Therefore, any particles larger than 0.8 times of the critical dimension of the features need to be removed. In one embodiment, the tapered end 105 of the collecting tip 104 has a diameter 108 slightly larger than the size 106 a of the particles 106 to be removed.

In one embodiment, the collecting tip 104 may be fabricated from a conductive material such as stainless steel and titanium.

Referring back to FIG. 1, the cleaning station 100 further comprises an indexing mechanism that provides relative movement between the collecting tip 104 and the substrate/mask 102 as shown by arrow 111. The relative movement allows the collecting tip 104 to access the entire top surface of the substrate/mask 102 to be cleaned. Embodiments of the indexing mechanisms are further described in FIGS. 3 and 4.

In one embodiment, the collecting tip 104 does not contact the substrate/mask 102 during the cleaning process. The distance 112 between the top surface of the substrate/mask 102 and the tapered end 105 of the collecting tip 104 may be less thank about 10 mm.

In another embodiment, the collecting tip 104 and the substrate/mask 102 may move relatively along the vertical direction as shown by arrow 113 of FIG. 1. The relative movement along the vertical direction allows the collecting tip 104 to approach the substrate/mask 102 for desired cleaning. In one embodiment, the collecting tip 104 may move close to the substrate/mask 102 to be in contact with the particles 106 to be cleaned during cleaning.

FIG. 3 schematically illustrates a perspective view of a cleaning station 200 in accordance with one embodiment of the present invention.

The cleaning station 200 generally comprises a frame 215, a collecting assembly 203 movably disposed on the frame 215, and a substrate support 201 configured to support a substrate/mask 202 thereon.

The collecting assembly 203 comprises a collecting tip 204 mounted on a mounting arm 209. The collecting tip 204 has a tapered end 205 free from the mounting arm 209 and facing the substrate support 201. The collecting tip 204 is electrically conductive and is coupled to an electrostatic source 207. The electrostatic source 207 is configured to provide electrostatic voltage to the collecting tip 204.

The mounting arm 209 has a free end 209 a where the collecting tip 204 is mounted and a fixed end 209 b coupled to the frame 215. The mounting arm 209 is rotatable about an axis 211 near the fixed end 209 b so that the free end 209 a and the collecting tip 204 are movable above the substrate support 201 as shown by curve 212. In one embodiment, the mounting arm 209 may also be movable along vertical direction as shown by arrow 216 to allow adjustment of elevations of the collecting tip 204.

The substrate support 201 is rotatable about a central axis 213. During a cleaning process, the substrate support 201 rotates about the central axis 213 while the mounting arm 209 moves along the curve 212 so that the collecting tip 204 scans through an entire surface of the substrate/mask 202.

The cleaning station 200 may further comprise a tip conditioning station 214 configured to remove collected particles from the collecting tip 204. In one embodiment, the tip conditioning station 214 may be disposed on the frame 215. Prior or after cleaning a substrate/mask, the mounting arm 209 may rotate towards the tip conditioning station 214 to have any particles on the collecting tip 204 removed.

FIG. 4 schematically illustrates a perspective view of a cleaning station 300 in accordance with another embodiment of the present invention.

The cleaning station 300 generally comprises an indexing stage 301 configured to movably support a substrate/mask 302 on a top surface 301 c. The indexing stage 301 comprises two drives 301 a, 301 b each configured to move the substrate/mask 302 independently along a direction.

The cleaning station 300 further comprises a collecting assembly 303 disposed about the stage 301. The collecting assembly 303 comprises a collecting tip 304 mounted on a mounting arm 309. The collecting tip 304 has a tapered end 305 free from the mounting arm 309 and facing the stage 301. The collecting tip 304 is electrically conductive and is coupled to an electrostatic source 307. The electrostatic source 307 is configured to provide electrostatic voltage to the collecting tip 304.

During cleaning, the substrate/mask 302 may be moved by the indexing stage 301 so that the collecting tip 304 can scan through the entire surface of the substrate/mask 302. Track 312 illustrates an exemplary scanning path for a cleaning process.

In one embodiment, the collecting tip 304 may be movable along vertical direction relative to the indexing stage 301 to allow adjustment of elevations of the collecting tip 304.

In one embodiment, the indexing stage 301 may move the substrate/mask 302 so that the collecting tip 304 is aligned with a particle 306 to be removed. In one embodiment, the collecting tip 304 may be lowered to contact the particle 306 during the removal.

FIG. 5 is a flow chart showing a cleaning process 400 in accordance with one embodiment of the present invention. The cleaning process 400 may be used during manufacturing of a mask for photolithography or manufacturing of semiconductor devices on a substrate.

Block 410 illustrates a pattern generating process wherein features are formed on a substrate or a mask by removing or depositing materials on certain areas.

Block 420 illustrates a wet cleaning process wherein residuals on the substrate or the mask from the pattern generating process are removed by a cleaning solution, such as a bulk cleaning solution. After wet cleaning, the substrate/mask should be fairly clean with only isolated particles remains thereon.

Block 430 illustrates an optional electrostatic cleaning process after the wet cleaning. The electrostatic cleaning may be scan cleaning using electrostatic cleaning stations described in accordance with embodiments of the present invention.

Block 440 illustrates an inspection process wherein the substrate/mask is probed to detect or locate any undesired particles.

Block 450 illustrates an electrostatic cleaning process after the inspection of block 440. The electrostatic cleaning may be a scan cleaning or a targeted cleaning using electrostatic cleaning stations described in accordance with embodiments of the present invention. A scan cleaning is when an electrostatically charged collecting tip scans the entire surface of the substrate/mask to remove any particles. A targeted cleaning is when an electrostatically charged collecting tip moves towards detected particles and picks the detected particles up. This electrostatic cleaning process is a fine cleaning compared to the wet cleaning process of block 420.

Block 460 illustrates another inspection process. Generally, the substrate/mask is ready for subsequent processing if no undesired particle is found in this inspection. However, if there are still remaining particles, process in blocks 450, 460 may be repeated.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. An apparatus for cleaning a substrate, comprising: a substrate support configured to receive and support the substrate; a collecting tip connected with an electrostatic power source, wherein the collecting tip is configured to pick up particles on a surface of the substrate using electrostatic force; and an indexing mechanism configured to provide relative movement between the collecting tip and the substrate support.
 2. The apparatus of claim 1, wherein the collecting tip comprises a tapered end pointing at the surface of the substrate.
 3. The apparatus of claim 2, wherein the size of the tapered end is determined according to the size of the particles to be picked up.
 4. The apparatus of claim 1, wherein the collecting tip is mounted near a moving end of a rotating arm and the indexing mechanism comprises an arm actuator configured to rotate the rotating arm about a fixed end of the rotating arm and to move the collecting tip above the substrate support.
 5. The apparatus of claim 4, wherein the indexing mechanism further comprises a support actuator configured to rotate the substrate support about a central axis of the substrate support.
 6. The apparatus of claim 1, wherein the indexing mechanism comprises a stage connected to the substrate support, and the stage is configured to move the substrate support along x and y coordinates.
 7. The apparatus of claim 1, wherein the electrostatic power source is configured to apply an electrostatic force between about 50 Volt to about 250 Volt to the collecting tip.
 8. The apparatus of claim 7, wherein the electrostatic force applied to the collecting tip is between about 50 Volt to about 100 Volt.
 9. An apparatus for removing particles from a substrate, comprising: a substrate support configured to receive and support the substrate; a probe assembly configured to remove particles from the substrate, wherein the probe assembly comprises: an arm having a free end and a fixed end, wherein the free end is movably disposed above the substrate support; a collecting tip mounted near the free end of the arm; and an electrostatic power source coupled to the collecting tip, wherein the electrostatic power source is configured to provide an electrostatic force to the collecting tip.
 10. The apparatus of claim 9, wherein the collecting tip has a tapered end, and a size of the tapered end is determined by the size of the particles to be removed.
 11. The apparatus of claim 9, wherein the substrate support is rotatable about a central axis of the substrate support, and the arm is rotatable about the fixed end.
 12. The apparatus of claim 9, further comprises an indexing stage coupled to the substrate support, wherein the two dimension stage is configured to move the substrate relative to the probe assembly.
 13. The apparatus of claim 9, wherein the electrostatic force is between about 50 volt to about 250 volt.
 14. The apparatus of claim 9, wherein the electrostatic force is between about 50 volt to about 100 volt.
 15. The apparatus of claim 9, wherein the substrate is a mask used in a lithography process during semiconductor processing.
 16. A method configured for cleaning a substrate, comprising: providing a collecting tip configured to pick up particles from the substrate; applying an electrostatic force to the collecting tip; and moving the collecting tip towards the particles on the substrate to pick up the particles.
 17. The method of claim 16, wherein providing a collecting tip comprises choosing a diameter of the collecting tip according to sizes of the particles to be picked up.
 18. The method of claim 16, wherein moving the collecting tip comprises: rotating the substrate about a central axis of the substrate while moving the collecting tip across the substrate from the central axis outwards.
 19. The method of claim 16, wherein moving the collecting tip comprises: scanning the substrate using the collecting tip.
 20. The method of claim 16, further comprising, prior to moving the collecting tip, inspecting the substrate to locate the particles.
 21. The method of claim 16, further comprising, prior to applying the electrostatic force, performing a wet cleaning to the substrate.
 22. The method of claim 16, wherein applying an electrostatic force comprises applying an electrostatic power between about 50 volt to about 250 volt to the collecting tip.
 23. The method of claim 22, wherein the electrostatic power is between about 50 volt to about 100 volt. 